This enzyme, found in several bacterial pathogens, is involved in degradation of the host’s cholesterol. It catalyses the hydroxylation of the C-26 carbon, followed by oxidation of the alcohol to the carboxylic acid via the aldehyde intermediate, initiating the degradation of the alkyl side-chain of cholesterol [4]. The products are exclusively in the (25S) configuration. It is a two-component system consisting of a P-450 (heme thiolate) oxygenase (Cyp125) and a ferredoxin reductase (most likely KshB, which is also a part of EC 1.14.13.142, 3-ketosteroid 9α-monooxygenase). The enzyme also accepts cholesterol as a substrate. cf. EC 1.14.13.221, cholest-4-en-3-one 27-monooxygenase.